I have never tried the silver bullet pipe but here are some of my notes that I use when tuning a pipe for its best performance, with the Irwin pipe the stinger length is good, I add just a little restriction of the stinger to create a little more back pressure, and heat. Hope this helps.
notes;
STINGERS Stinger length should be separated from stinger diameter because although they are linked, in practice you would need to make a big change in stinger length to affect the backpressure. Stinger diameter is crucial to the pipes operating temperature and hence the power production. If the stinger is bigger than optimum them making it even bigger will have little effect but by sleeving it down then you will be able to find the size that gives best power. Normally a smaller stinger will improve top end power because the exhaust gas temperature will increase which will have the effect of a shorter pipe length. If you go too small on the stinger then power will suddenly start to drop in the corners and the motor will begin to overheat. To get the best power its usual to lengthen the header and make the stinger smaller to get the best overall performance. A bigger stinger will have the effect of spreading the power band but the engine will not make the same peak hp.
Stinger length is important because its part of the pipe resonance. The wrong stinger length will reduce performance at the upper end of the rpm band. i.e. between peak torque and peak bhp.. There will be maybe one or two stinger lengths that will cut the rpm off at a certain level reducing the 'overrev' which gives the best top speed. There will be one stinger length which gives the best overall power and overrev. I find no way to calculate that stinger length, trial and error is the only way. Its not dependent upon engine size, just on the pipe design. For example, my best .21 pipe runs over 100 mm stinger but my best .90 runs around 60mm. One thing though, very short stingers up to 40mm long don't normally work and extremely long stingers of 150mm to 200 mm can work very well. Once the best stinger length is found, it does not seem to vary if the pipe length is altered.
